I've not heard of "all kinds of local seed exchanges". This year I only knew of the one I held a few weeks ago. So far I've not heard of any others.
Tomatoes: Tomatoes do not always produce lycopine in heat - lycopine is needed for ripening, so what MRice says is absolutely true. Last year I had to wait for some, but most were good. I grow a huge variety including Juliette, yellow pear, cherokee purple, black krim, marlglobe, rutgers, San Marsano, roma, sungold and many many more.
Bell Peppers: I love sweet peppers and there are tons of great sweet peppers that are not bells. However I really like Yolo Wonder, it produces well as do some Italian frying peppers like Corno De Toro. Key: They need really good soil that is fairly high in phosphates. Plant your peppers on the East side of your tomatoes. They'll get Am sun and PM shade and do well.
Potatoes: Plant soon
March 31 at the East Atlanta public library Mary Yetter, Brooks Garcia (Robby Astrove will be doing fruit on the Sunday...more classes are being scheduled those days, so look for it! and I are holding gardening workshops for just $10. I will be doing a vegetable gardening workshop.). Funds are to raise money for the library!!